1. Field of the Invention
The present invention relates to fluid exchangers for exchanging transmission fluid in an automatic transmission.
2. Description of the Prior Art
It has long been recognized that the transmission fluid in automatic transmissions should be exchanged periodically to remove impurities and provide new clean effective transmission fluid. Many efforts have been made to provide a satisfactory device to achieve this function in an efficient and convenient manner.
It has been recognized that benefit may be taken of the transmission pump itself to pump used fluid from the transmission to a used fluid tank while simultaneously pumping new fluid into the transmission upstream of the transmission pump. Typically, some automobile transmissions incorporate a bypass which protects the transmission from overpressurization. This bypass may be effective to relieve pressure in the event the pump pumping used fluid in should overpressurize the transmission. However, not all transmissions incorporate this internal bypass arrangement and there exists a risk of overpressurizing the transmission.
One effort to solve the fluid exchange problem led to the development of a fluid exchanger mounted on a small cart and having inlet and outlet control valves for controlling the rate at which fluid is pumped into the transmission. Such exchangers typically employ rather elaborate plumbing which may allow for pressure relief in the event a certain pressure is exceeded. A device of this type is shown in U.S. Pat. No. 5,370,160 to Parker and assigned to the assignee of the instant application. Such devices, while having enjoyed substantial commercial success, are relatively expensive to manufacture and are somewhat bulky to store and use.
Other efforts have led to the proposal of a small hand held exchanger including fluid pumps and valves for controlling flow to and from the automatic transmission. A device of this type is shown in my U.S. Pat. No. 5,743,357 and assigned to the owner of the assignee of the instant application. While providing significant benefits, such devices suffer the shortcoming that there is no provision to prevent overpressurization of the transmission.
Other efforts have been made to sense transmission pressures and equalize such pressures to avoid overpressurization. One such device incorporates a rather elaborate pre-exchange adapter purportedly used for sensing the pressure in the transmission. Efforts have then been made to balance the inlet and outlet pressures from such transmission across a diaphragm or piston. A device of this type is shown in U.S. Pat. No. 5,472,064 to Viken. While offering some benefits, such devices still suffer the shortcoming that use thereof is relatively time consuming and the systems involve the risk that diaphragm or piston, under high pressure, may result in damage and substantial spillage.
Thus, there exists a need for a transmission fluid exchanger which eliminates the expense of incorporating a fluid pump and which protects the transmission against overpressurization. Other benefits could be derived from providing for a single hook up which would allow for sensing of the transmission pressure by a single gauge which could also be used for sensing the pressure differential during the exchange procedure.